Reflective plate and method for manufacturing the same and backlight unit for liquid crystal display device using the same

ABSTRACT

A reflective plate includes a high heat conductivity material having a first heat conductivity and a reflective material having a second heat conductivity on the high heat conductivity material, wherein the first heat conductivity of the high heat conductivity material is greater than the second heat conductivity of the reflective material.

This application claims the benefit of the Patent Korean Application No.P2006-003190 filed on Jan. 11, 2006, P2005-080231 filed on Aug. 30,2005, and P2006-009638 filed on Feb. 1, 2006, which are herebyincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to reflecting light, and moreparticularly, to a reflective plate and method for manufacturing thesame and a backlight unit for a liquid crystal display (LCD) deviceusing the same. Although the embodiments of the invention are suitablefor a wide scope of applications, it is particularly suitable formaintaining uniformity of temperature across a reflective plate and amethod for manufacturing the same, and a backlight unit for an LCDdevice using the same.

2. Discussion of the Related Art

In general, a liquid crystal display device includes a liquid crystaldisplay module, a driving circuit for driving the liquid crystal displaymodule, and a case for protecting the driving circuit and the liquidcrystal display module. The liquid crystal display module has a liquidcrystal display panel having a matrix of liquid crystal cells in whichliquid crystal is injected into a gap between two bonded glasssubstrates. Switching devices are positioned in each of the liquidcrystal cells for switching signals applied to the liquid crystal cells.The liquid crystal display module also includes a backlight unit forproviding light to the back side of the liquid crystal display panel.Optical sheets for scattering and diffusing the light from the backlightunit are positioned between the liquid crystal display panel and thebacklight unit.

The liquid crystal display panel, the backlight unit, and the opticalsheets of the liquid crystal display module are packaged together toprevent light leakage and to protect these components from an externalimpact. The glass substrates of the liquid crystal display panel in theliquid crystal display module are susceptible to damage due to anexternal impact. A top case is used to package the backlight unit andthe optical sheets together with the liquid crystal display panel.Further, the top case runs along the edges of the liquid crystal displaypanel such that the liquid crystal display panel can still be viewed.Accordingly, the top case protects the glass substrates of the liquidcrystal display panel in the liquid crystal display module from anexternal impact.

FIG. 1 is an exploded perspective view of the related art liquid crystaldisplay device. As shown in FIG. 1, the liquid crystal display device 10includes a liquid crystal display panel 20, and a backlight unit 30 forproviding light to the liquid crystal display panel 20. The backlightunit 30 includes a fluorescent lamp 31 for emitting light, a lamphousing 32 surrounding the fluorescent lamp 31 in a U shape, a lightplate 33 for distributing light from the fluorescent lamp 31, and areflective plate 34 for reflecting light into the light plate 33. Aprotective sheet 35, a first prism 36, a second prism 37 and diffusionsheets 38 are positioned in succession on the light plate 33. A bottomcover 39 for receiving and holding both the liquid crystal display panel20 and the backlight unit 30.

The backlight unit 30 provides light to a display region A of the liquidcrystal display panel 20. The display region A of the liquid crystaldisplay panel 20 has a matrix of liquid crystal cells (not shown) inwhich liquid crystal (not shown) is injected into a gap between twobonded glass substrates (not shown). The liquid crystal display device10 also includes a driving circuit 40 for driving the liquid crystaldisplay panel 20.

When the fluorescent lamp 31 at one edge of the light plate 33 emitslight, the lamp housing 32 focuses and directs the light toward an edgeof the light plate 33. Then, the light from the edge of the light platespreads throughout the entire surface of the light plate 33 and isredirected toward the display region A of the liquid crystal displaypanel 30 through the protective sheet 35, the first prism 36, the secondprism 37 and the diffusion sheets 38. A thin film transistor on theliquid crystal display panel controls transmission of the light througha pixel in response to a signal from the driving circuit of the liquidcrystal display device. Together, the pixels display a picture on thedisplay region of the liquid crystal display panel.

FIG. 2 is a plan view of the related art backlight unit, and FIG. 3 is across-sectional view of the related art backlight unit in FIG. 2 alongline II-II′. As shown in FIGS. 2 and 3, the related art backlight unit50 includes a lamp 51 for emitting light, a lamp housing 52 for holdingthe lamp 51 and reflecting light from the lamp 51 toward one direction,and a light plate 53 for distributing the light from the lamp 51 into aplanar light and providing the planar light to a liquid crystal displaypanel (not shown). The related art backlight unit 50 also includes areflective plate 54 on a back side of the light plate 53 for reflectingthe light toward the liquid crystal display panel, an optical sheet 55on the light plate 53 for enhancing a luminance of the light, and acover bottom 56 for supporting an assembly of the lamp housing 52 andthe light plate 53. The reflective plate 54 under the light plate 53re-reflects light directed thereto through a bottom surface of the lightplate 53, thereby increasing light utilization efficiency.

The lamp 51 is typically a cold cathode fluorescent lamp, and the lightplate 53 has a scattering pattern (not shown) formed at a predeterminedportion thereof for scattering light and a reflecting portion (notshown) in which the light is internally reflected. The light plate 53has a display region (not shown) and a non-display region (not shown).Light entering into the light plate 53 through a light incident surfaceat an edge of the light plate 53 from the lamp 51 advances toward thedisplay region of the light plate 53 through the non-display region inwhich the light is internally reflected. The light is scattered by thescattering pattern in the display region.

FIG. 4 is a cross-sectional view of the lamp housing in the related artbacklight unit. Referring to FIG. 4, the lamp housing 52 has aluminum(Al) film 52 a and a reflective film 52 b, such as polypropylene (PP) orPolyethylene Terephthalate (PET), bonded together with an adhesive 52 c.The reflective film 52 b is placed on an inner side of the lamp housing52 and the aluminum film 52 a is placed on an outer side of the lamphousing 52. More specifically, the reflective film 52 b portion is onthe inner side of the lamp housing 52 for reflecting the light from thelamp 51 in one direction, and the aluminum film 52 a is on the outerside for dissipating heat from the lamp 51 to outside of the liquidcrystal display panel. The reflective plate 52 of the related artbacklight unit is a reflective film, such as polypropylene (PP) orPolyethylene Terephthalate (PET), coated onto a back side of the lightplate 53.

Because the backlight unit has the reflective film on the inside of thelamp housing and on the backside of the light plate, heat from the lampcan not efficiently dissipate to the bottom cover through the lamphousing. In effect, the reflective films act as insulation. Thus, heatbuilds up within the backlight unit that effects the liquid crystaldisplay panel. Such heat build-up can cause deformation of thecomponents within the liquid crystal display panel. Moreover,deformation of the optical sheet and the large view angle polarizationplate of a LCD device causes light leakage at upper and lower corners ofthe display panel.

SUMMARY OF THE INVENTION

Accordingly, embodiments of the invention are directed to a reflectiveplate and method for manufacturing the same and backlight unit for aliquid crystal display (LCD) device using the same that substantiallyobviates one or more of the problems due to limitations anddisadvantages of the related art.

An object of embodiments of the invention is to provide a reflectiveplate which can effectively dissipate heat from the lamp of a backlightto outside of the liquid crystal display panel.

Another object of embodiments of the invention is to provide a methodfor manufacturing a reflective plate which can effectively dissipateheat from the lamp of a backlight to outside of the liquid crystaldisplay panel.

Another object of embodiments of the invention is to provide a liquidcrystal display (LCD) device using a backlight unit with a reflectiveplate which can effectively dissipate heat from the lamp of a backlightto outside of the liquid crystal display panel.

Additional advantages, objects, and features of embodiments of theinvention will be set forth in part in the description which follows andin part will become apparent to those having ordinary skill in the artupon examination of the following or may be learned from practice of theinvention. The objectives and other advantages of embodiments of theinvention may be realized and attained by the structure particularlypointed out in the written description and claims hereof as well as theappended drawings.

To achieve these objects and other advantages and in accordance withembodiments of the invention, as embodied and broadly described herein,a reflective plate includes a high heat conductivity material having afirst heat conductivity and a reflective material having a second heatconductivity on the high heat conductivity material, wherein the firstheat conductivity of the high heat conductivity material is greater thanthe second heat conductivity of the reflective material.

In another aspect, a method for manufacturing a reflective plateincludes providing a heat dissipation plate of high heat conductivitymaterial having a first heat conductivity and forming a reflectivematerial having a second heat conductivity on the high heat conductivitymaterial, wherein the first heat conductivity is greater than the secondheat conductivity.

In another aspect, a method for manufacturing a reflective plateincludes providing a heat dissipation base, placing a heat dissipationplate of high heat conductivity material having a first heatconductivity on the heat dissipation base, and placing a reflectivematerial having a second heat conductivity on the high heat conductivitymaterial, wherein the first heat conductivity is greater than the secondheat conductivity.

In another aspect, a backlight unit includes a lamp for emitting light,a light plate for distributing the light from the lamp into a planarlight and directing the planar light to a liquid crystal display panel,a lamp housing for reflecting the light from the lamp onto a lightincident surface at an edge of the light plate, a reflective platehaving a stack of a high heat conductivity material with a first heatconductivity and a reflective material having a second heat conductivityon a back side of the light plate, and a bottom cover for supporting thelamp housing and the light plate, wherein the first heat conductivity isgreater than the second heat conductivity.

In another aspect, a backlight unit includes a plurality of lamps foremitting light, a cover bottom for supporting and receiving theplurality of lamps, an optical sheet for covering an upper surface ofthe bottom cover and diffusing the light from the plurality of lamps,and a reflective plate having a stack of a high heat conductivitymaterial with a first heat conductivity and a reflective material with asecond heat conductivity on an inside surface of the bottom cover forreflecting the light from the plurality of lamps toward the opticalsheet, wherein the first heat conductivity is greater than the secondheat conductivity.

In another aspect, a liquid crystal display device includes a liquidcrystal display panel for displaying a picture, a lamp for emittinglight, a light plate for distributing the light from the lamp into aplanar light and directing the planar light to a liquid crystal displaypanel, a lamp housing for reflecting the light from the lamp onto alight incident surface at an edge of the light plate, a reflective platehaving a stack of high heat conductivity material with a first heatconductivity and a reflective material having a second heat conductivityon a back side of the light plate, and a bottom cover for supporting thelamp housing and the light plate, wherein the first heat conductivity isgreater than the second heat conductivity.

In yet another aspect, a liquid crystal display device includes aplurality of lamps for emitting light, a cover bottom for supporting andreceiving the plurality of lamps, an optical sheet for covering an uppersurface of the bottom cover and diffusing the light from the pluralityof lamps, and a reflective plate having a stack of a high heatconductivity material with a first heat conductivity and a reflectivematerial with a second heat conductivity on an inside surface of thebottom cover for reflecting the light from the plurality of lamps towardthe optical sheet, wherein the first heat conductivity is greater thanthe second heat conductivity, and a liquid crystal display panel overthe optical sheet for receiving the light through the optical sheet todisplay a picture.

It is to be understood that both the foregoing general description andthe following detailed description of embodiments of the invention areexemplary and explanatory and are intended to provide furtherexplanation of embodiments of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is an exploded perspective view of the related art liquid crystaldisplay device;

FIG. 2 is a plan view of the related art backlight unit;

FIG. 3 is a cross-sectional view of the related art backlight unit inFIG. 2 along the line II-II′;

FIG. 4 is a cross-sectional view of the lamp housing in the related artbacklight unit;

FIGS. 5A to 5C illustrate cross-section views each showing a reflectiveplate in accordance with embodiments of the invention;

FIG. 6 is a perspective view of a backlight unit in accordance with anembodiment of the invention;

FIG. 7 is a cross-sectional view of a backlight unit in accordance withanother embodiment of the invention; and

FIG. 8 illustrates a graph showing a comparison of reflection ratios(total reflection characteristics) of the related art reflective plateand a functional reflective plate of embodiments of the inventiondepending on refractive indices of adhesives in the respectivereflective plates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIGS. 5A to 5C illustrate cross-sectional views each showing areflective plate in accordance with embodiments of the invention. Asshown in FIG. 5A, a reflective plate 500 a is on a buffer layer 540. Thereflective plate 500 a includes a reflective material 520 on a high heatconductivity material. A high heat conductivity material is a materialthat has a higher heat conductivity than the heat conductivity of thereflective material 520. In addition, a shielding layer (not shown) maybe provided between the reflective material 520 and the high heatconductivity material 510 as a buffer between the reflective material520 and for improving stiffness of the reflective plate.

The high heat conductivity material 510 can be at least one of graphite,aluminum, copper, carbon nano tube (CNT), and AlSiC in a sheet, plate orpowder form. The high heat conductivity material 510 can have athickness of about 0.08 mm ˜0.20 mm. The reflective material 520 can beat least one of Ag, Al₂O₃, TiO₂, Al, PET (Polyethylene Terephthalate),and an optical fiber. The reflective material 520 is coated with ascattering material applied thereon. The reflective material 520 canhave a thickness of 150˜250 μm if the reflective material is used for amonitor, and have a thickness of 115˜225 μm if the reflective materialis used for a notebook PC. A plurality of diffusion beads 522 in adiffusion material 523 can be coated on the reflective material 520,such as an AlNd layer, to improve the reflection ratio, as shown in FIG.5A. The reflective plate 500 a is formed by depositing the reflectivematerial 520 on the high heat conductivity material 510 through a plasmavapor deposition (PVD) or sputtering process such that the high heatconductivity material 510 and the reflective material 520 are laminatedtogether.

In the alternative, as shown in FIG. 5B, the reflective material 520 andthe high heat conductivity material 510 of a reflective plate 500 b canbe bonded with an adhesive 530. For example, the adhesive 530 may be atwo sided adhesive tape. If a refractive index of the adhesive 530 issmall, a large reflection ratio can be maintained even if a thickness ofthe reflective material 520 is small. Because of the use of the highheat conductivity material 510, such as graphite, the high heatconductivity material 510 can have a thickness less than the reflectivematerial 520. The buffer layer 540 covers bottom and side surfaces ofthe high heat conductivity material 510 to prevent the high heatconductivity material 510 from leaking to outside of the backlight unitand to guard against foreign matters from infiltrating into the highheat conductivity material 510.

For example, the high heat conductivity material 510 can have athickness of 60˜120 μm, the adhesive 530 can have a thickness of 20˜40μm, and the reflective material 520 can have a thickness of 60˜100 μm.In addition, a shielding layer (not shown) may be provided between thereflective material 520 and the high heat conductivity material 510 as abuffer between the reflective material 520 and for improving stiffness.The reflective plate 500 b can be fabricated by placing the high heatconductivity material 510, the adhesive 530, and the reflective materialin succession on the buffer layer 540.

In another alternative, as shown in FIG. 5C, a reflective plate 500 ccan be a reflective material 520 with shielding layer 550 stacked on thehigh heat conductivity material 510. The shielding layer 550 providesstiffness to the reflective material 520. By attaching the shieldinglayer 550 to the reflective material 520, the reflective material 520and the high heat conductivity material can be manufactured separatelyand then brought together for assembly.

FIG. 6 illustrates a perspective view of a backlight unit in accordancewith an embodiment of the invention. Referring to FIG. 6, the backlightunit 600 includes a lamp 601 for emitting light, a light plate 602 fordistributing the light from the lamp 601 into a planar light andproviding the planar light to a liquid crystal display panel (notshown), a lamp housing 603 having a stack of a high heat conductivitymaterial and a reflective material for positioning the lamp 601 at anedge of the light plate 602 to reflect the light from the lamp 601 ontoan edge surface of the light plate 602, a reflective plate 605 having astack of a high heat conductivity material and a reflective material ona back side of the light plate 602 and at another edge surface of thelight plate 602 opposite to the edge surface of the light plate 602receiving light for reflecting the light toward a liquid crystal displaypanel 607, an optical sheet 604 on the light plate 602 for enhancingluminance of the light, and a bottom cover 606 for supporting anassembly of the lamp housing 603 and the light plate 602.

The lamp 601 is typically a cold cathode fluorescent lamp, and the lightplate 602 has a scattering pattern formed at a predetermined portionthereof for scattering the light reflected on an inside, and is alsoprovided with a display region and a non-display region. The lightenters into the light plate 602 through a light incident surface at anedge of the light plate 602 from the lamp 601 and proceeds toward thedisplay region through the non-display region while the light isinternally reflected. Light emits through an upper surface of the lightplate 602 so as to provide a planar light source as a result of lightbeing dispersed by the scattering pattern of the light plate 602 andbeing internally reflected within the light plate 602.

The lamp housing 603 and the bottom cover 606 are the heat dissipationbases of the backlight unit 600. The reflective plate 605 having thestack of a high heat conductivity material and a reflective material onthe lamp housing 603 and the bottom cover 606 enable the backlight unitin embodiments of the invention to dissipate heat from the lamp 601through the lamp housing 603 and the bottom cover bottom 606. Thereflective plate 605 may extend to an upper surface of the light plate602 at the edge opposite to the light incident surface of the lightplate 602. The lamp 601 may be red, green, and blue light emittingdiodes, a plurality of white light emitting diodes, EEFL (ExternalElectrode Fluorescent Lamp) or a CCFL (Cold Cathode Fluorescent Lamp).

The optical sheet 604 can include a diffusion sheet (not shown), atleast one prism sheet (not shown), and a protective sheet (not shown)stacked on the light plate 602 in succession. The diffusion sheetoptimizes uniformity and orientation of the light from an upper surfaceof the light plate 602. The prism sheet converges light from thediffusion sheet to an intended direction, such as toward an LCD panel607, to form a uniform picture. The protective sheet protects the prismsheet and diverges light output so as to increase a viewing angle of theplanar light source.

FIG. 7 illustrates a cross-sectional view of a backlight unit inaccordance with another embodiment of the invention. As shown in FIG. 7,the backlight unit 700 includes a plurality of lamps 701 for emittinglight, a bottom cover 702 for receiving the plurality of lamps 701, anoptical sheet 703 over the bottom cover 702 for diffusing and convergingthe light from the plurality of lamps 701, and a liquid crystal displaypanel 704 for receiving the light from the optical sheet 703 to displaya picture.

The lamps 701 are typically cold cathode fluorescent lamps. Theplurality of lamps 701 are lit by a lamp driving voltage from aninverter (not shown) so that the backlight unit emits light to a backside of the optical sheet 703. Moreover, the bottom cover 702 not onlysupports but also receives the plurality of lamps 701. A reflectiveplate 705 having a stack of a high heat conductivity material and areflective material for reflecting the light from the plurality of lamps701 toward the optical sheet 703 is attached to an inside surface of thebottom cover 702 of the backlight unit 700. The optical sheet 703includes a diffusion plate (not shown) covering an upper surface of thebottom cover bottom 702 and diffusing the light from the plurality oflamps 701, and a prism sheet (not shown) on the diffusion sheet forconverging the light from the diffusion plate.

FIG. 8 illustrates a graph showing a comparison of reflection ratios(total reflection characteristics) of the related art reflective plateand a functional reflective plate of embodiments of the inventiondepending on refractive indices of adhesives in the respectivereflective plates. As shown in FIG. 8, the reflection ratio A of therelated art reflective plate has a minimum of 0.178, a maximum of 0.914,and an average of 0.291. However, the reflection ratio B of thefunctional reflective plate in an embodiment of the invention has aminimum of 0.190, a maximum of 0.908, and an average of 0.276 when therefractive index of the adhesive in the functional reflective plate is1.41. Moreover, the reflection ratio C of the functional reflectiveplate in an embodiment of the invention is a minimum of 0.221, a maximumof 0.908, and an average of 0.303 when the refractive index of theadhesive in the functional reflective plate is 1.30.

Although the reflection ratio of the functional reflective plate of anembodiment of the invention is 0.276 on average, which is lower than therelated art if a general adhesive of PET or the like with a refractiveindex 1.41 is used to adhere a reflective plate, the reflection ratio ofthe reflective plate can be greater than or the same as the related artreflective plate on average if the refractive index of the generaladhesive is less than 1.30. Further, overall thickness of the reflectiveplate can be reduced by using an adhesive having a lower refractiveindex since the reflection ratio increases without having to increasethe thickness of the reflective material.

Table 1 shows refractive indices of various adhesives for differentwavelengths in nanometers.

PMMA Polystyrene Polycarb SAN PET NAS TPFE 365.0 nm 1.5136 1.6431 1.64321.6165 — — — 404.7 nm 1.5066 1.6253 1.6224 1.5971 — — — 435.8 nm 1.50261.6154 1.6115 1.5886 — — — 480.0 nm 1.4983 1.6052 1.6007 1.5800 1.6870 —— 486.1 nm 1.4978 1.6041 1.5994 1.5790 — 1.5740 — 546.1 nm 1.4938 1.59501.5901 1.5713 1.6680 — — 587.6 nm 1.4918 1.5905 1.5855 1.5674 1.6600 — —589.3 nm 1.4917 1.5903 1.5853 1.5673 — 1.5640 1.3100 643.9 nm 1.48961.5858 1.5807 1.5634 1.6510 — — 656.3 nm 1.4892 1.5949 1.5799 1.5627 —1.5580 — 706.5 nm 1.4878 1.5820 1.5768 1.5601 — — 852.1 nm 1.4850 1.57621.5710 1.5551 — — 1014.0 nm  1.4831 1.5726 1.5672 1.5519 — —

A lamp housing with a reflective plate having high heat conductivitymaterial enables effective dissipation of the heat from the lamp to anoutside of the liquid crystal display device through the cover bottom toprevent luminance drop and deformation of optical components caused bytemperature rise. By applying an adhesive having lower refractive indexbetween a high heat conductivity material and the reflective material ofthe reflective plate, total thickness of the reflective plate can bereduced because a large reflection ratio can be maintained with areflective material having a small thickness.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the embodiments of theinvention without departing from the spirit or scope of the inventions.Thus, it is intended that the present invention covers the modificationsand variations of this invention provided they come within the scope ofthe appended claims and their equivalents.

What is claimed is:
 1. A reflective plate comprising: a high heatconductivity material; a reflective material having a shielding layer ona bottom of the reflective material for shielding and improvingstiffness; an adhesive having a small refractive index between the highheat conductivity material and the reflective material, wherein theadhesive bonds the high heat conductivity material and the reflectivematerial; wherein the reflective material is at least one of Ag, Al₂O₃,TiO₂, Al, Polyethylene Terephthalate, and optical fiber, wherein thereflective material is coated with a scattering material including aplurality of diffusion beads applied thereon, wherein the high heatconductivity material is at least one of graphite and carbon nano tube(CNT) in a form of sheet, plate or powder, and wherein the adhesive isformed of TPFE that has refractive index of 1.31 when wavelength is589.3 nm.
 2. The reflective plate of claim 1, wherein the reflectivematerial and the high heat conductivity material are joined by PVD,sputtering, laminating, or coating.
 3. The reflective plate of claim 1,further comprising a protective layer for covering an underside and aback surface of the high heat conductivity material.